NUDT5-Determines the fate of head and neck squamous cell carcinoma cells under endoplasmic reticulum stress by catalyzing nuclear ATP production to promote DNA repair

NUDT5 is the only discovered enzyme that catalyses ATP production in cell nuclei. In this study, we investigate the character of NUDT5 in head and neck squamous cell carcinoma (HNSCC) cells under endoplasmic reticulum (ER) stress. The formation of ER stress was confirmed in HNSCC cells using Real-time PCR and Western blot techniques. The expression of NUDT5 was modified by transfecting HNSCC cells with siRNA and plasmids, respectively. The effects of NUDT5 manipulation were assessed using various methods including cell counting kit-8 assay, western blotting, RNA sequencing, Immunofluorescence Microscopy analysis, cell cycle analysis and nucleic ATP measurement, and a xenograft mouse model. In this study, we found that the expression of NUDT5 proteins was upregulated under ER stress conditions in HNSCC cells. Knocking down NUDT5 under ER stress could hinder nuclear ATP generation and thus induce more DNA damage and apoptosis of HNSCC cells. Only the wild-type NUDT5 or ATP catalysis active mutant T45A-NUDT5, rather than the ATP catalysis null mutant T45D-NUDT5, could directly rescue nuclear ATP depletion caused by NUDT5 inhibition and protect HNSCC cells from DNA damage and cell apoptosis. Finally, in vivo studies showed that knocking down NUDT5 in ER-stressed conditions could significantly inhibit tumour growth. Our study demonstrated for the first time that NUDT5 guaranteed the integrity of DNA under ER stress-triggered DNA damage by catalysing nuclear ATP production. Our findings offer new insights into how the energy supply in cell nuclei fuels cancer cell survival in stressful microenvironment.